1. Technical Field
The present disclosure relates to testing in general, and to a method and apparatus for digitally testing a pair of converters, in particular.
2. Discussion of the Related Art
When conducting tests of an electronic device, testing should be performed to the level of a replaceable component, i.e., if a particular component comprises two or more sub-components which are not individually fixed or replaced, it is enough to test the component as one unit, and there is no particular importance to pinning down the malfunctioning sub-component. Since testing should be performed as cheap and efficient as possible, then testing such a component as one unit, if designed correctly may save specialized equipment and separate tests and thus increase the testing efficiency.
When testing a combined converter unit comprising a Digital-to-Analog Converter (DAC) and an Analog-to-Digital Converter (ADC), if the two converters are not to be replaced or fixed separately, it is beneficial to test them together, by feeding digital data into the DAC, feeding the analog output of the DAC into the ADC, and digitally testing the digital output of the ADC. Using this scheme, it is not required to generate or test analog signals, thus saving on analog testing equipment and on testing time.
However, when testing the two converters together, even if both are functional, their characteristics indicating the output voltage vs. the input voltage may not be one-to-one, and moreover may not match each other. Thus, the output of such a unit comprising a pair of converters may deviate from the input although both components are functional.
Consider for example FIG. 1, showing a graphical representation of two non-matching converters, in which horizontal axe 104 indicates the digital values, and vertical axe 108 indicates the analog values. Line 112 represents the transfer function of one converter, and line 116 represents the reverse transfer function of the other converter. Although both lines are shown on the same coordinate system it will be appreciated by person skilled in the art that for one converter axe 104 represents the input and axe 108 represents the output, and vice versa for the other converter. Since the two lines do not coincide, then there is an offset-value 120 and a gain-difference 124 between them. Once offset 120 and gain-difference 124 are known, they can be compensated for and the unit comprising the two converters can then be tested.
There is thus a need for a method and apparatus for detecting the offset and gain between a converter pair consisting of connected digital-to-analog converter DAC and an analog-to-digital converter, so that the unit as a whole can be tested for proper functionality, using digital equipment only.